The 雅道 Gadou style of display places emphasis on display of Shohin trees in a seki kazari format...most of the scrolls paired with these are in the Rinpo Hyougu style, which can be quite long. 5-6 feet...

So the size of the tree seems to not be your limiting factor, but the size of your display area, hence wanting the smaller size scroll...

Golden Arrow Bonsai http://www.goldenarrowbonsai.com/goldenarrowbonsai.com/Home.html purchased a really small scroll from me but it was not really designed for display purposes in mind...